Process and device for compensation of the effect of roll eccentricities

ABSTRACT

A process and device for compensation of the effect of roll eccentricities upon thickness regulation of material being rolled in a roll stand (1), wherein eccentricity oscillations are simulated by a model (6) based on measured values of roll adjustment position (s), roll force (F W ) and mean support roll speed (n), together with spring constants (C G , C M ) for the roll stand and the material. An output signal (Δ R ) of the model (6) is used to modify the thickness value (h a  +ΔR) used for regulation, so as to compensate for the effect of roll eccentricity. The model may be implemented by a device (RECO) comprising pairs of oscillators (7), the phase and amplitude relationships of which are adjusted according to the observer principle.

The invention relates to a process and a device for compensation of theeffect of roll eccentricities in position- or thickness regulation ofroll stands.

According to U.S. Pat. No. 3,928,994 it is known to eliminate, by amethod of autocorrelation, the effect of roll (roller or cylinder)eccentricities on a signal used for an actual value of stand elasticity.Another component of the indirectly formed actual value signal, namelyroll (positional) adjustment, is not affected by this, so that with thisknown process, compensation of the effect of roll eccentricities is onlypartially achieved. Furthermore, because of the mean value formationsused therein, autocorrelation methods always entail a time expenditurewhich limits the speed of response of thickness regulation.

According to the present invention there is provided a process forcompensation of the effect of roll eccentricities in position orthickness regulation of a roll stand, comprising steps of:

(a) forming a sum signal from a measured value of a roll forcemultiplied by the sum of the inverse values of a stand spring constantand a material spring constant, and a measured value of a rolladjustment position;

(b) sending the sum signal through a high pass filter a frequency ofwhich is adjusted in dependence upon a speed of a support roll of theroll stand;

(c) comparing an output signal of the high pass filter with a sum outputsignal of at least one pair of oscillators, said oscillators beingprovided for simulation of roll eccentricity oscillations, andfrequencies of said oscillations being preset in dependence upon theradius of the support roll and being adjusted in dependence upon thesupport roll speed;

(d) adjusting the oscillators in respect of amplitude and phaserelationship so that a deviation between the output signal of the highpass filter and the sum output signal of the oscillators is at aminimum; and

(e) subtracting the sum output signal of the oscillators from an actualvalue signal of position or thickness.

According to the present invention there is provided a device forcompensation of the effect of roll eccentricities in position orthickness regulation of roll stands, comprising:

a multiplier for receiving as a first input the measured value of theroll force and as a second input the sum of the inverse values of thestand spring constant and the material spring constant, and formultiplying its first and second inputs together;

a mixer for adding together the measured value of the roll adjustmentposition and the output of the multiplier;

the high pass filter, for subtracting from the signal output from themixer a component corresponding to a steady part of an incomingthickness value of material to be rolled by the roll stand; and a modelportion comprising said oscillators, provided for simulatingoscillations caused by roll eccentricities of the roll stand, a mixerfor comparing the sum output signal of the oscillators with the outputof the high pass filter, for producing the deviation and for supplyingthe deviation to the oscillators to enable adjustment of the oscillatorsin respect of amplitude and phase relationship in order to minimise thedeviation, and an output for supplying the sum output signal of theoscillators.

An embodiment of the invention can provide a process for compensation ofroll eccentricities during position or thickness regulation of rollstands, which can work both more accurately and more quickly than knownprocesses, and which utilises measuring devices commonly present on rollstands.

An embodiment of the invention can provide a process for compensation ofroll eccentricities comprising indirect actual value formation effectedby determination of roll stand elasticity.

Reference is made, by way of example, to the accompanying Figures inwhich:

FIG. 1 schematic diagram of an arrangement comprising a rolleccentricity compensator (RECO) in accordance with an embodiment of thepresent invention for enabling thickness regulation of a roll stand,

FIG. 2 is a schematic diagram of the basic structure of the rolleccentricity compensator of FIG. 2,

FIG. 3 is a schematic diagram of an embodiment of a model for simulatinga pair of roll eccentricity oscillations effected in a roll eccentricitycompensator,

FIG. 4 is a schematic diagram for explaining signal processing in amodel with several simulated pairs of eccentricity oscillations,

FIG. 5. is a schematic diagram of the construction of a rolleccentricity compensator for a process using digital signal processing.

In FIG. 1 there is schematically shown a roll stand (rolling machine) 1.The roll stand comprises an upper support roll (roller or cylinder) withradius R_(o), a lower support roll with radius R_(u), two worker rollshaving a smaller radius than the support rolls, a hydraulic piston forproviding positional adjustment of the upper support roll, and ahydraulic cylinder associated with the piston which is supported on thestand structure. The elasticity (resilience) of the stand structure isshown symbolically by a spring with a spring constant C_(G). Thematerial for rolling has associated with it, in a roll gap between thetwo worker rolls, an equivalent material spring with a spring constantC_(M). The material is rolled by means of the two worker rolls from arun-in thickness h_(e) down to a run-out thickness h_(a).

Roll eccentricities of the upper or the lower support roll may arise dueto uneven wear of the rolls, deformations due to heat stresses, ordeviations in the geometrical cylinder axes of the rolls from theoperationally adjusted axes of rotation. The roll eccentricities of theupper and lower support rolls are designated ΔR_(o) and ΔR_(u),respectively, i.e. as deviations from the ideal support roll radii R_(o)or R_(u).

The roll stand further comprises a number of measurement transducers;these are provided for detecting the support roll speed n (normally inthe form of a tachodynamo (electric speed indicator) coupled to thedrive motor), for detecting a roll force F_(w) exerted by the hydraulicpiston, and for detecting a roll adjustment position which correspondsto the relative position s of the piston in the hydraulic cylinder usedfor adjusting the upper support roll. In addition, 2 indicates a controlelement by means of which the hydraulic piston is acted on by pressureoil by means of a valve. A regulating signal for the control element isprovided by an output signal of a regulator 3 whose purpose is to bringthe thickness h_(a) of the outgoing roller material into conformity witha desired thickness value h_(a) * supplied to it.

The value of the actual thickness value h_(a) of the band (sheet, stripor layer) of rolled material is not measured directly at its origin,i.e. in the roll gap, but is determined from the roll stand elasticityand the roll adjustment position. For this purpose a device known as agauge meter, designated GM in FIG. 1, is used. This device basicallycontains a multiplying device which (in a known process) multiplies themeasured value of roll force F_(W) with the inverse value of the standspring constant C_(G) and adds to this product the measurement valuesignal s of the relative hydraulic piston position. Between the inputsignals and the output signal of the device GM the followingrelationship holds:

    h.sub.a +ΔR =s +F.sub.W /C.sub.G,

wherein the superimposed effects of the two support roll eccentricitiesΔR_(o) and ΔR_(u) are combined within the term ΔR.

The arrangement described so far corresponds substantially to a knownarrangement for band thickness (rolled material thickness) regulationwith determination of the actual thickness value h_(a) being carried outaccording to the gauge meter principle. However, in known arrangements,in the presence of a roll eccentricity ΔR the gauge meter GM does notsupply the actual thickness value h_(a) alone but rather the sum of theband thickness and the roll eccentricity. Band thickness regulationusing the gauge meter signal (h_(a) +ΔR) as the actual value iseffective for controlling changes in the band run-in thickness into theroll stand, but acts incorrectly with regard to roll eccentricities.This is because a thickness regulation on the basis of an output signalh_(a) +ΔR of the gauge meter GM as an actual thickness value is carriedout exactly like a thickness regulation with h_(a) as an actualthickness value and a desired value h_(a) * -ΔR, so that the thicknessregulation incorrectly causes the eccentricity ΔR to be rolled in to thematerial band with run-out thickness h_(a), phase shifted by 180°. Thisis unsatisfactory because the greatest values of eccentricities canamount to several tens of micrometers, which is not compatible withpresent day tolerance requirements for a cold-rolled band.

Therefore, in an embodiment of the present invention, a compensationdevice called a RECO (roll eccentricity compensator) is used, whosepurpose is to identify or simulate a roll eccentricity ΔR usingmeasurement transducer signals s, n and F_(W) supplied to it, and theadjustment parameters R_(o), R_(u), C_(G) and C_(M). The signal ΔRsimulated by the compensation device is used to clear up (correct) theadulterated actual value of the band run-out thickness supplied by thegauge meter GM, so that the true actual thickness value h_(a) occurringin the roll gap can be supplied to the regulator 3. Exact compensationof the effect of the roll eccentricities ΔR can thereby be achieved. Thestand spring constant C_(G) is determined once in a test before startingrolling operation and the material spring constant C_(M) is determinedby running on-line calculation. The operation of the RECO device wasbased on the inventors' insight that for an exact simulation of rolleccentricities, the roll stand positional adjustment, the roll standelasticity, and also the elastic deformation of the material during theroll process, should all be taken into account.

A compensation device in accordance with the invention can also be usedwith similar advantages for pure position regulation. In this case thegauge meter GM is omitted. The output signal of the compensation deviceRECO is subtracted from the measurement value signal s, and the resultis used as an actual position value. Instead of the desired valueh_(a) * of the run-out thickness, a desired position value is fed to theregulator 3.

FIG. 2 shows the basic construction of a roll eccentricity compensatorRECO in an embodiment of the present invention.

The compensator contains a multiplier 4 to which are fed on the inputside the roll force measurement signal F_(W) and the sum of the inversevalues of the stand spring constant C_(G) and the material springconstant C_(M). This inverse value sum corresponds to the inverse valueof a spring constant resulting from the series arrangement of theelasticity of the roll stand and the elasticity of the rolled material.

The position measurement value s of the hydraulic piston adjusting theupper support roll is added to the output signal of the multiplier 4 ina mixer 5. The output signal of the mixer 5 represents the sum of theeccentricity signal ΔR caused by the eccentricities ΔR_(o) and ΔR_(u),and the band run-in thickness value h_(e), wherein the latter consistsof a direct (steady) part h_(e) and a statistically deviatingalternating part h_(e) superimposed on this. The equation h_(e) =h_(e)+h_(e) therefore applies. By means of a high pass filter HF, the steadypart h_(e) of the run-in thickness h_(e) is subtracted from the outputsignal of the mixer 5, so that at the output of the high pass filter HF,which is updated in its (angular)(cut-off) frequency by the speedmeasurement value n, there is produced the signal ΔR+h_(e).

From this signal, in an arrangement 6 designed according to the observerprinciple, a signal ΔR is simulated which corresponds to the rolleccentricity. The arrangement 6 constitutes a back-coupled (retroactive)model for the eccentricity disturbances ΔR. The arrangement 6 comprisesat least two oscillators (7) for the fundamental oscillations, occurringin pairs, of the eccentricities ΔR_(o) and ΔR_(u) of the upper or thelower support roll, and in the case of pairs of relevant higherfrequency oscillations (harmonics) occurring also, is suitablysupplemented by appropriate further pairs of oscillators.

The frequencies of the oscillators are determined by inputs of thesupport roll radii R_(o) and R_(u) and of the mean support roll speed n.The outputs of the individual oscillators are combined to form asummation signal ΔR and are compared with the output signal of the highpass filter HF in a mixer 8. The deviation signal e produced from thiscomparison is used to adjust the oscillations produced by theoscillators as regards their phase relationships and amplitudes, untilthe signal ΔR is a copy of the eccentricity oscillation ΔR. This is thecase when the deviation e is at a minimum and corresponds only to thestatistically fluctuating portion h_(e) of the run-in thickness h_(e).Frequency adaptation is thus effected continuously during rollingoperations in dependence on the support roll speed n, and the (angular)(cut-off) frequency of the high pass filter HF is correspondinglyentrained.

FIG. 3 shows an example embodiment of a model 6 for simulating the rolleccentricity ΔR, having a pair of oscillators for the simulation ofeccentricity-based oscillations.

Each oscillator is formed by a pair of integrators 9, 10 or 11, 12,wherein in each pair one integrator is arranged behind the other, andthe output signal of the integrator 10 or 12 is counter-coupled to theinput of integrator 9 or 11, respectively. At the input of eachintegrator there is arranged a multiplier 13, 14, 15 or 16, by which thefrequencies of the oscillators are determined. A second input of eachmultiplier is acted upon by a signal n corresponding to the mean supportroll speed. The components determining the time behaviour of theintegrators are made to be adjustable, for example by using rotarypotentiometers or variable capacitors. These components are adjustedaccording to the determined values of the radii R_(o) or R_(u) of thesupport rolls, and in accordance with the support roll speed n.

The outputs of the integrators 10 and 12 are added in a mixer 17, whoseoutput signal is subtracted from the output signal ΔR +h_(e) of the highpass filter HF in a further mixer 18. The deviation e is thus obtained,by means of which the oscillations produced by the oscillators 9, 10 or11, 12 are adjusted in respect of phase relationships and amplitudes bymeans of proportional elements a to d, until the summation signal ΔR ofthe integrators 10 and 12 agrees with the part ΔR, due to the rolleccentricity, of the input signal (ΔR +h_(e)) supplied to thedisturbance model 6.

The parallel arrangement of two pairs of oscillators (integrators) shownin FIG. 3 can be converted into a functionally equivalent seriesconnection by the use of known transformation rules. A filter of fourthorder type can be recommended for many cases of usages (for the highpass filter HF).

FIG. 4 shows the structure of a disturbance model 6 in the rolleccentricity compensator RECO for a case in which three higher frequencyoscillations (harmonics) are to be considered as relevant, apart fromthe basic (fundamental) oscillations of the roll eccentricity.

The model has four parts which are similar in construction andreferenced 60, 61, 62 and 63 in FIG. 4. Each of the parts 60, 61, 62 and63 is constructed in accordance with FIG. 3 and contains a pair ofoscillators. Thus a pair of oscillators is provided for the basicoscillations and for the first, second and third harmonic oscillationsrespectively. The individual eccentricity simulations produced by theparts 60, 61, 62 and 63, designated ΔR_(o), ΔR₁, ΔR₂ and ΔR₃respectively, are superimposed to give a resulting simulation of theentire eccentricity ΔR. Phase- and amplitude adjustment of theoscillators in each part 60, 61, 62 and 63 is effected in dependenceupon individual deviations e_(o), e₁, e₂, e₃. For each oscillator twoadjustment amplifications (proportional elements) a_(o), b_(o) or c_(o),d_(o) are necessary, as is shown for the basic oscillation pair of themodel part 60.

FIG. 5 shows the construction of a roll eccentricity compensator RECOusing a digitally operating micro computer 19, in accordance with anembodiment of the present invention. In this embodiment, signalprocessing is effected by supplying input signals via two analog/digitalconverters 20 and 21 and supplying output signals via a digital/analogconverter 22. The microcomputer 19 is divided into three functionalblocks 191 to 193. In block 191, after input of values for the twosupport roll radii R_(o) and R_(u) and input of a nominal mean supportroll speed, calculation of oscillator-frequencies to be preset takesplace offline. In block 192, which contains a signal processor, signalprocessing for simulation of the roll eccentricity ΔR takes place bymeans of oscillators in accordance with the arrangements of FIGS. 3 or4, but converted into a functionally equivalent digital implementation.Signal processing takes place in known manner, with the values of theinput signals being sampled at discrete time intervals and a simulationresult being output at corresponding time intervals. A reconstructionfilter RF is provided immediately after the digital-analog converter 22,so as to convert the stepped analog result sequence obtained at discretetime intervals into a time-continuous signal. Since the block 192 may beconsidered in practice as a digital filter, a so-called anti-aliasingfilter AF is inserted after the high pass filter HF so as to avoidoutput signal distortion (aliasing noise) cause by sampling of inputsignals with frequency components too high relative to the samplingrate. Anti-aliasing filters, such as are described for example in the"2920 Analog Signal Processor Design Handbook" published by the IntelCorporation 1980, on page 2 - 1 to page 2 - 5, are low pass filterswhich have a high damping (attenuation), for example as much as 60 dB,at a frequency corresponding to half the sampling rate. The filters HF,AF and RF, which comprise a combination of integrators and summingamplifiers (integrating amplifiers), are as before updated in their(angular) (operating or cut-off) frequencies in dependence upon thesupport roll speed n. This can be achieved by means of multipliersprovided at inputs of the integrators of the filters, such as in thearrangement of FIG. 3.

The block 193 contains a timer which adjusts the frequency of theoscillators in block 192, constructed by digital means, in dependence onthe actual support roll speed n. The timer may, for example, be acounter that can be preset to the output value of the analog-digitalconverter 20. Such a counter is constantly counted down at a fixed clockrate, and outputs a pulse (for frequency adjustment) to the signalprocessor 192 each time a zero count is reached.

We claim:
 1. A process for compensation of the effect of rolleccentricities in position or thickness regulation of a roll stand,comprising steps of:(a) forming a sum signal from a measured value of aroll force (F_(W)) multiplied by the sum of the inverse values of astand spring constant (C_(G)) and a material spring constant (C_(M)),and a measured value of a roll adjustment position (s); (b) sending thesum signal through a high pass filter (HF) a frequency of which isadjusted in dependence upon a speed (n) of a support roll of the rollstand; (c) comparing an output signal of the high pass filter with a sumoutput signal of at least one pair of oscillators, said oscillatorsbeing provided for simulation of roll eccentricity oscillations, andfrequencies of said oscillators being preset in dependence upon theradius of the support roll and being adjusted in dependence upon thesupport roll speed (n); (d) adjusting the oscillators in respect ofamplitude and phase relationship so that a deviation (e) between theoutput signal of the high pass filter and the sum output signal of theoscillators is at a minimum; and (e) subtracting the sum output signal(ΔR) of the oscillators from an actual value signal of position orthickness.
 2. A process according to claim 1, wherein for simulation ofhigher frequency roll eccentricity oscillations, additional pairs ofoscillators are provided, sum output signals of which are alsosubtracted from the actual value signal.
 3. A process according to claim1, for regulation of the thickness of outgoing material rolled by theroll stand, wherein at step (e) the sum output signal (ΔR) of theoscillators is subtracted from an actual value signal (h_(a) +ΔR) ofthickness to produce a corrected actual value of thickness, and furthercomprising steps of:(f) comparing the corrected actual value ofthickness with a desired value of thickness (h_(a) *); and (g) supplyingthe result of the comparison of step (f) as input to a regulator (3)provided for controlling a control element (2), thereby to adjust theroll adjustment position (s) in order to achieve thickness regulation ofthe outgoing material.
 4. A roll eccentricity compensator for use in theprocess according to any of claims 1 to 3, comprising:a multiplier (4)for receiving as a first input the measured value of the roll force(F_(W)) and as a second input the sum of the inverse values of the standspring constant (C_(G)) and the material spring constant (C_(M)), andfor multiplying its first (F_(W)) and second inputs together; a mixer(5) for adding together the measured value of the roll adjustmentposition (s) and the output of the multiplier (4); the high pass filter(HF), for subtracting from the signal output from the mixer (5) acomponent corresponding to a steady part of an incoming thickness value(h_(e)) of material to be rolled by the roll stand; and a model portion(6) comprising said oscillators, provided for simulating oscillationscaused by roll eccentricities of the roll stand, a mixer (8) forcomparing the sum output signal of the oscillators with the output ofthe high pass filter (HF), for producing the deviation (e) and forsupplying the deviation (e) to the oscillators to enable adjustment ofthe oscillators in respect of amplitude and phase relationship in orderto minimise the deviation (e), and an output for supplying the sumoutput signal (ΔR) of the oscillators.
 5. A roll eccentricitycompensator for use in the process according to any of claims 1 to 3,wherein for the simulation of eccentricity oscillations there isprovided a signal processor (192) operable as a digital filter, withwhich there is associated, via an analog-digital converter, a timer(193) which in operation is influenced by the mean support roll speed(n).
 6. A roll eccentricity compensator according to claim 5,comprising: a multiplier (4) for multiplying together the measured valueof the roll force (F_(W)) and a value based on the stand spring constant(C_(G)) and the material spring constant (C_(M)),a mixer (5) for addingthe measured value of the roll adjustment position (s) to the output ofthe multiplier (4), the high pass filter (HF), for subtracting from theoutput of the mixer (5) a signal component corresponding to a steadypart of an incoming thickness value (h_(e)) of material to be rolled bythe roll stand, an anti-aliasing filter (AF), a frequency of which canbe adjusted in dependence upon the support roll speed (n), for carryingout low-pass filtering of the output of the high pass filter (HF); ananalog-digital converter (21) for converting the output of theanti-aliasing filter into a digital form; a microcomputer (19)comprising a portion (191) for calculating oscillator frequencies, thesignal processor (192) for providing the at least one pair ofoscillators, and the timer (193); the analog-digital converter (20); adigital-analog converter (22) for converting the output of the signalprocessor (192) into analog form; and a reconstruction filter (RF) forsmoothing the output of the digital-analog converter (22) into atimecontinuous signal.
 7. A process according to claims 1, 2 or 3,wherein the roll stand is of a type which comprises an upper supportroll, a worker roll in contact with the upper support roll, a lowersupport roll, and a worker roll in contact with the lower support roll.